An ink jet head used in an ink jet printer includes an insulating substrate formed of a ceramic material, a nozzle plate arranged to be opposed to the insulating substrate, a driving element arranged to be stacked between the insulating substrate and the nozzle plate, a frame member made of a ceramic material that surrounds the driving element to form a common liquid chamber and pressure chambers.
The driving element includes a pair of piezoelectric elements made of a PZT (lead titanate zirconate) piezoelectric ceramic material. The driving element is driven by a driving circuit. An electrode pattern that makes the driving element and the driving circuit conductive is formed on the insulating substrate. Taper surfaces are formed on both end faces of the driving element.
In the ink jet head in the past, the electrode pattern that makes the driving element and the driving circuit conductive is formed on the insulating substrate. An electrode is formed by, for example, well-known electroless plating. For the electroless plating, chemical pretreatment such as adsorption of catalytic cores is necessary. The electrode pattern is formed to extend from the driving element to the insulating substrate. Therefore, the piezoelectric element and the insulating substrate are simultaneously subjected to the electroless plating.
Therefore, it is requested that the surfaces of the piezoelectric element and the insulating substrate have similar characteristics with respect to the chemical pretreatment. If chemical characteristics of the surfaces of the piezoelectric element and the insulating substrate are substantially different, a difference occurs in deposition of a plating film and the plating film peels in a later process.
Further, since the electrode pattern having thickness of several tens micrometers is drawn around on the surface of the insulating substrate, smoothness and absence of an air gap are also requested. If the smoothness is poor and the air gap is present, the electrode pattern is inadvertently open.
Moreover, after the piezoelectric element is joined to the insulating substrate, if the end faces of the driving element are mechanically tapered, the insulating substrate side is also machined. However, if mechanical characteristics of the surfaces of the piezoelectric element and the insulating substrate are substantially different, cracks and chips occur in the piezoelectric element and the insulating substrate.
On the other hand, because of the request for a reduction in cost of the ink jet head, it is desirable that even an insulating substrate that has less satisfactory smoothness and in which a large number of air gaps are present can be used.